The rainfall-no rainfall transition in a coupled land-convective atmosphere system

A one-dimensional representation of the atmospheric boundary layer (ABL) depth is coupled to a soil moisture bucket model to dynamically explore the relative roles of surface and free atmospheric conditions on convective precipitation occurrence and resulting soil moisture states. This occurrence is taken to depend on the crossing of the ABL height and the lifting condensation level in the presence of pure convective instability. If rainfall occurs (unrealistically) whenever these conditions are met, and free atmospheric conditions are constant, the resulting system state evolves towards a limit cycle with precipitation every day or every few days, or to a completely dry state. The free atmospheric humidity profile has a larger effect on determining the stationary soil moisture state than the temperature profile. The effect of dry air entrainment on surface energy partitioning decreases soil moisture sensitivity to free atmospheric conditions. © 2010 by the American Geophysical Union.